The overall objective of this project is to characterize the circulating proinsulin and C-peptide components in normal individuals, obese non-diabetics, obese diabetics, "honeymoon-phase" type I diabetics, and selected patients with insulinomas. Proinsulin components will be collected by affinity chromatography from 100-200 ml of preserved plasma collected during the basal state and after pancreatic stimulation with glucose or glucagon to selectively maximize the release of newly synthesized or stored proinsulin components. Following immunopurification, further separation of the components by differences in charged amino acid content will be performed by disc-gel polyacrylamide electrophoresis. These purified materials will be subjected to enzymatic modifications to identify the presence and location of basic amino acids. The attachments of C-peptide to insulin will be identified by gel filtering sulfitolyzed, purified material and identifying C-peptide and insulin B-chain in the various gel filtration fractions. These circulating proinsulin components are products of the B-cell proinsulin conversion process and will demonstrate the behavior of that system during selected forms of "stress", abnormal glucose metabolism and disorders of insulin synthesis. Particular attention will be paid to various types of diabetes in an attempt to identify subtypes marked by an unusual circulatory proinsulin component or relatively increased amounts of a proinsulin-like material. Characterization of proinsulin components in certain subjects with insulinoma may reflect a direct disorder of proinsulin modification, structurally deranged proinsulin-like material or simply the effects of "overloading" the B-cell conversion process.